The present invention relates generally to an approach for developing pharmaceuticals and treatment protocols that are effective against Candida-associated pathologies.
Fungal diseases have become a major medical problem and are growing in severity, given the rising incidence of immunosuppression associated with AIDS, diabetes, cancer therapies, and organ transplantation, among other conditions. Debilitated patients thus affected are especially susceptible to fungal pathogens, most of which are opportunists.
The yeast Candida can exist both as a non-virulent colonizer (commensal) and as a pathogen. Candidiasis is increasingly widespread, with hospitalized and immunocompromised patients at greatest risk, and has become the sixth most common form of pathogenic infection. Systemic Candida infections may be lethal, with a mortality rate of 50% in adults and up to 65% in infants. Reviewed in Pfaller (1996); see also Colombo et al. (1999). The risk of death from systemic infection most strongly correlates with the time between the first detected infection and the onset of anti-fungal treatment. Pacheco-Rios et al. (1997).
The pathogenic success of Candida depends in part upon phenotypic plasticity. The most prominent Candida pathogen, C. albicans, exhibits a bud-hypha phenotype transition that occurs en masse, in response to various stimuli, and provides C. albicans with the capacity to penetrate tissue and to disseminate. Odds (1997). Candida albicans also undergoes spontaneous, reversible, high frequency switching of phenotypes, which does not occur en masse.
More specifically, C. albicans may switch reversibly between a phenotype characterized by white colonies and a phenotype characterized by opaque colonies. Soll (1992). This white/opaque switching occurs at higher frequencies in isolates from deep versus superficial mycoses, Jones et al. (1994), at higher frequencies in infecting versus commensal isolates from the oral cavity, Hellstein et al. (1993), within sites of infection, Soll et al. (1987), (1988), and within sites of commensalism, Soll (1992). Switching also has been shown to regulate virulence in animal models. Kvaal et al. (1999).
High-frequency phenotypic switching in C. albicans involves the coordinated regulation of a battery of phase-specific genes. The gene products of several of these genes facilitate pathogenesis, Soll (1992) and Soll (1996). These products include secreted aspartyl proteinases, Hube et al. (1994), Morrow et al. (1992), (1993) and White et al. (1993), and drug resistance proteins, Balan et al. (1997).
Switching provides a mechanism for enhancing pathogenesis via generation of phenotypic plasticity. Thus, switching results in antigenic variability on the yeast cell surface. No single phenotypic trait has been found to be responsible for Candida pathogenesis, however. Moreover, uncertainty has surrounded the extent of overlap in respective regulatory circuitry for the switching event (white⇄opaque) and the dimorphism event (hypha⇄budding cell), as well as the significance of such overlap to Candida pathogenesis.
With the emergence of drug-resistant Candida strains and a growing population of immunocompromised individuals, there is an mounting need to find new treatments for candidiasis.
In light of this need and others, the present invention has provided, in one aspect, a method for screening a therapeutic agent, comprising subjecting a first Candida culture to the agent and then determining the impact thereof on expression of a gene in the TUP1 pathway, such as SAP3, OP4 and TUP1 itself, whereby decreased expression of the gene is predictive of efficacy for said agent against candidiasis. In a preferred embodiment, the aforementioned determination comprises gauging expression of the gene by reference to the level of Tup1 protein or TUP1 transcript in the first culture.